For practice, as Hugh says, you need to be able to provide quality passes and crosses, retain a high amount of pace and have some fancy footwork to go with it. Personally as a winger/holding midfielder I've been practising juggling and general tricks in the off-season, as well as going down to the field and the grounds at my mum's school and practising crossing and FK's against the wall. Sprinting and running as well as general fitness training shall begin after my knees have cleared up after surgery this thursday.

Which wing do you play on, and are you two footed or one? Personally I love being partially two-footed (right-footed but can still dribble, cross, partially take FK's with my left) and playing on either wing as it befuddles your opposition, push for their weaker side and gogogo!! Playing on the left Wing is a hell of alot of fun as you can always take the option of either a) crossing or b) cutting inside the defender for a shot on goal.

I would say the main concern you should have would be stamina. You'll have to be running up and down the field for a full 90 minutes, so you need to be quite fit. Also, wingers are generally fast, able to beat opponents down the sideline, often by simply out running them. I recommend that you start a fitness program if you have not already. For more specific information on what you do here, just ask.

On defense- you'll want to make sure that as soon as your team loses possession, and you aren't in a position to win the ball back, run back and, depending on your team's tactics, towards the middle. Generally, your job would be to make sure to close down your counterpart winger to limit crosses, shots, and penetrating passes. You should be in or near the box to clear out crosses, and once your team has regained possession, to run forward.

On offense- you want to be wide for passes and through balls to the corner. Be able to beat your marker down the line and get a cross in. When the ball is on the other side of the pitch then be in the box ready to finish service. You don't always have to cross in, you can thread passes to strikers, back to the CM, and when you're facing a defender on your team, pass it to them and make a looping run.